The invention relates to a vehicle cryo tank for storing a cryo fuel in a motor vehicle, comprising an internal storage container and an external container, enveloping said internal container, so as to form an insulating vacuum, whereby heat input from the outside into or at the internal container can be switched on or off. The invention further relates to a method for using the same. For the technical environment reference is made to DE 195 46 618 C2 as an example.
Searching for alternative drive energies for motor vehicles, one is also working with liquefied gases in general and with hydrogen in particular. In this respect a liquefied gas (for example, liquefied natural gas) or hydrogen in the liquid form is stored in a so-called cryo tank. Different lines, in which there are, for example, valves, but also heat exchangers or elements of the tank system that generally convey fluid, lead into the tank or out of the tank, thus, among other things, to the fuel operated internal combustion engine.
Fuel, which is gaseous under normal ambient conditions, is stored in a highly cooled state in a container, which is called here an internal container, of a cryo tank that is enveloped by a container, which is called here an external container, to minimize thermal input. In this case the space between the internal container and the external container is largely evacuated. On the other hand, a targeted thermal input into the interior of the internal storage container is necessary and thus into the fuel stored therein, because the tank is always supposed to have an adequate quantity of gaseous fuel, after the fuel is fed in the gaseous state to the internal combustion engine.
In the known prior art, the desired thermal input into the internal container occurs by means of an electrically operated heating element, which is disposed inside said internal container. To supply the heating element with energy, lines must be run into and out of the cryo tank. The same also applies to another method of targeted thermal input, where already gaseous fuel is guided through the still fluid fuel. Here, too, for the targeted introduction of the gaseous fuel, at least one separate pipe line with switching valves and/or the like is necessary.
Even if in these known systems no heat input is supposed to occur in the internal storage container, the said lines act as an already existing thermal bridge, over which a small, but not ignorable quantity of heat can get to the stored fuel, a state that is fundamentally undesired. Another drawback of these known systems lies in their hysteresis behavior, in particular when turning off. That is, after the targeted thermal input is turned off, heat is fed on a significant scale in an undesired manner to the stored fuel for a certain period of time.
The object of the present invention is to provide a measure to remedy this described problem.
The solution to this problem is characterized in that there is a switch selectable thermal bridge element, over which a heat conducting connection between the wall of the internal container as well as the wall of the external container can be produced or interrupted. Further advantageous designs and improvements are discussed below.
According to the invention, a special element is provided virtually between the internal container and the external container and thus in the insulating vacuum, with which this insulating vacuum can be bridged so as to be switch selectable. This so-called thermal bridge element can be changed over and can thus be moved from a so-called closed position, in which it produces a heat conducting connection between the wall of the internal container and the wall of the external container, into an opened position, in which this connection is interrupted and thus the insulating vacuum is not bridged. Like a plug-socket connection or an electric switch or the like, the thermal bridge element can exhibit a so-called receiving element, fastened to the outside of the wall of the internal container, as well as a so-called output element, fastened to the inside of the wall of the external container. Of these two elements at least one can be moved relative to the other.
As long as the receiving element and the output element are separated from each other and thus are not connected together so as to conduct or transfer heat, there is certainly no thermal input of virtually any kind (with the exception of thermal radiation) over this thermal bridge element into the cryo tank or any supply of heat to the fuel stored therein. In particular, then heat cannot be supplied over lines, which are, in fact, blocked, but, nevertheless, lead into the storage space of the internal container, to the fuel therein. The aforementioned continuous heat input, which may in deed be low, but still not ignorable, into the cryo tank over special lines, provided specifically to supply heat to the cryo tank, cannot take place, if such a targeted supply of heat is not desired. Not until and only as long as this thermal bridge element is closed, does such a targeted heat input into the system occur, as desired. If thereafter the thermal bridge element is opened, the supply of heat is stopped almost suddenly, in particular if the receiving element, assigned to the internal container, has a relatively low thermal capacity. In this sense the so-called receiving element of the internal container can have a lower thermal capacity and/or a smaller size than the output element, assigned to the external container.
Like a relay, the switch selectable thermal bridge element can be changed over electromagnetically. A related electric line to supply the switch selectable electromagnet has to lead only to the so-called output element, which is provided on the external container, but not to the so-called receiving element, which is provided on the internal container, so that the desired effect, namely no thermal bridge in the form of a continuous electric line, is still guaranteed.
Whereas in the opened state of this thermal bridge element, there is, as desired, no heat input of any kind into the system or into the fuel stored therein, when the thermal bridge element is closed, an optimal supply of heat to the cryo fuel stored in the internal container is desired. To achieve this state, the switch selectable thermal bridge element can be designed in such a manner that in the closed state a spatial (and not just linear) contact area or the heat transfer area is formed between the receiving element and the output element of the switch selectable thermal bridge element. For example, in the so-called closed state of the thermal bridge element a conical pin or the like of the output element can project into a corresponding receptacle of the receiving element and in so doing come to lie as completely as possible against the corresponding receiving wall.
Similarly with respect to an optimized heat transfer between the output element and the receiving element at least one of these elements can be designed in such a manner so as to be flexible or variable in shape that in the closed state of the thermal bridge element adequate heat transfer is guaranteed. In so doing in the closed state these two elements are pressed against each other. For example, the output element can vary in shape so that in the closed state of the thermal bridge element it clamps the receiving element between itself.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.